This invention relates to a bin, hopper or ship""s cargo hold discharge gate used in controlling the flow of a particulate material out of the bottom of the bin, hopper, or cargo hold.
The cargo spaces of ships adapted to convey particulate solids in bulk, generally known as bulk carriers, generally comprise a series of cargo holds which are in many ways similar to bulk bins or hoppers used in other applications to contain similar particulate solids. In this context, by xe2x80x9cparticulate solidsxe2x80x9d is meant any particulate solid material which is normally conveyed in bulk, in high volume; typical examples are crushed coal, many mineral ores including powdered sulphur, crushed rock, salt, fertilisers, saltpetre and various types of grain. These materials are well adapted to being moved about by continuous feed machinery, typically including the use of continuous belt conveyors, bucket elevators, and the like. These materials also vary in size and bulk density from wheat, which is relatively small and of low bulk density, to minerals which can be about 20 cm or more in diameter and have a relatively high bulk density.
Although a relatively small bin, or hopper, for example as used in a truck or rail car, fitted with a gate mechanism can be emptied from the bottom relatively easily, emptying a relatively large space, such as the sections of a bulk storage facility or the holds of a bulk carrier ship, poses additional problems. In a so-called xe2x80x9cself unloadingxe2x80x9d bulk carrier, the discharge gate system is located in the bottom of each hold, which serves both to close the bottom of the hold, and, when opened, to allow transfer of the hold contents onto a first conveyor means located in a tunnel under the cargo holds. The conveyor moves the received solids along the tunnel, beneath the holds, to an elevator means which is generally at one end of the bulk cargo space, for example in the hull forecastle. The elevator moves the particulate solids essentially vertically, to a point from which they can be discharged from the ship, generally carried by a second conveyor means. In some self unloading bulk carriers each cargo hold can include two or three gate systems, together with the required tunnels and conveyers. Similar underfloor installations are used in bulk storage facilities.
In many self unloading bulk carriers the discharge gate system in each hold comprises a row of centre opening gates, so-called xe2x80x9cbasket gatesxe2x80x9d, generally located so that the central axis of opening is along the length of the conveyor beneath the gate. The bottom of the hold is tapered downwardly to the row of gates to facilitate solids flow. The length of the gate opening can be from 1 meter to 10 meters, with most gates being in the range of from about 2 meters to 7 meters. The width of the aperture when the gate is open can also be up to 2 meters.
Each basket gate mechanism typically includes two opposed gate segments, and a hydraulic cylinder system to move the segments to open and to close the gate aperture; it is also possible to use linear electrically powered actuators or pneumatic cylinders instead of hydraulic devices. A feature common to all so-called basket gates currently in use is that the gate segments move together and provide equal opening about the centre line of the gate opening; this is usually ensured by linking the segments together by a coordination mechanism. Several coordination mechanisms have been described, including lever systems (see e.g. Ward, U.S. Pat. No. 2,284,781; Leonardi et al., U.S. Pat. No. 4,844,292; Gloucester R.C and W. Co., GB 2 081 198; Elder et al., WO 99/46187; Lorgard, WO 94/04444; and Dominium Magnesium Ltd, GB 1,175,179) hydraulic and pneumatic systems (see e.g. Suykens, U.S. Pat. No. 3,704,797; Hartmann Manuf. Co, GB 1,196,531; and Allis-Chalmers, GB 1,538,183) and gear systems (see e.g. Elder, WO 99/46187). The gate segments have to be substantial structures, as they have to support the load imposed by the cargo when closed, which also means that significant force can be required to move the gate segments.
Although gate openings have increased in length and width, the construction of the basket gate has hardly changed. Each box-like elongate gate segment is mounted between frames which support the top ends of the links carrying the gate segments, the mechanisms used to coordinate gate segment movement, and the hydraulic cylinders used to move them; other than at the ends of a row of basket gates, each frame generally supports the ends of two adjacent gates. The frames and mechanisms between each gate are supported by structures in the bottom of each cargo hold, and are protected by a covering structure, known as a hog back. In the known basket gate, the hydraulic system is arranged to act onto either the coordination mechanism, the ends of the gate segments directly, or at more or less the midpoint of the gate segments, with the result that for each gate at least two, and often four, hydraulic cylinders are required, which both increases first cost and hydraulic installation complexity (especially if a remote control system is used), and requires significant maintenance. Additionally, in the known basket gate systems, the conveyor placed below the gate to receive discharged solids operates at only one preset constant speed. It then follows that the only practical way to control the rate at which particulate solid material is discharged from a selected hold is to control carefully the width of the gate opening, either by separate local manipulation of each gate, or by remote control. In a bulk carrier this requires either an operative to work in an inhospitable and relatively inaccessible space, or a sophisticated control system operating a complex hydraulic system to move the gate segments. Although the control system can usually be located in a reasonably protected space, the hydraulic system is located in the tunnel under the holds, with the consequence that the hydraulic system is located in an aggressive environment and at a location in which maintenance is not easy. Similar problems arise in the construction and operation of gate discharge systems used in sub-floor locations in bulk storage facilities.
A need therefore exists for a simpler, less complex, and more compact basket gate discharge system, which will occupy a smaller space, which provides a measure of discharge rate control, and which does not require a complex hydraulic system. Such a mechanism will have applicability more generally in bulk holding bins, silos, hoppers and rail cars, and more particularly in bulk storage facilities and bulk cargo carriers.
This invention seeks to provide such a mechanism. In the basket gate according to this invention, the hydraulic system is simplified, and constructed to locate the gate in only three positions: closed, open to an operating position to discharge solids, and fully open to a clean-out position; double acting hydraulic cylinders attached between the gate ends are used to move the gate segments. The movement of the gate segments is preferably coordinated by a gear system, which can be small and compact. Additionally, the longitudinal axis of the gate is located at a small angle relative to the plane defined by the conveyor belt beneath the gate, so that the downstream end of both the gate opening and the hold opening is somewhat wider than the upstream end. In order to compensate for this angle, the mechanisms at each end of the gate which support and coordinate movement of the gate segments provide for differential movement of the gate ends so that torsional twisting of the gate segments is substantially avoided. As a further flow control measure, the downstream ends of each of the gate segments are provided with overlapping shear plates, which define the maximum depth of particulate solid which can be deposited onto the conveyor beneath the gate. The overall space requirements for the basket gate are diminished, since the supporting frames and the hog back needed to protect them are smaller, and the gate structure as a whole is significantly simplified.
In an installation designed and used for only one product, the operating position of the gate segments is chosen to provide a suitable particulate solid flow rate. In order to control the discharge rate for an installation used for several products, the conveyor control system is modified to allow the linear speed of the conveyor to be varied.
Thus in its broadest embodiment this invention seeks to provide an angled discharge gate mechanism, for use in conjunction with a hopper having at least one bottom opening, the bottom opening having an upstream end and a downstream end, through which particulate solid material discharges onto a conveyor located beneath the opening and extending along the longitudinal axis of the opening, the conveyor moving in a downstream direction, the gate mechanism including a pair of gate segments supported at their ends by linkages attached at first ends to a supporting structure and at second ends to the gate segments, which linkages also include gate segment movement coordination means, and a hydraulic system constructed and arranged to move the gate segments to provide a discharge aperture, where the hydraulic system is constructed and arranged to locate the gate segments in a position chosen from the group consisting of fully closed, operating, and clean out the longitudinal axis of the gate is located at an angle of from about 0.5xc2x0 to about 5xc2x0 relative to the plane defined by the conveyor, the hopper bottom opening is located at the same angle of from about 0.5xc2x0 to about 5xc2x0 relative to the plane defined by the conveyor, the hopper bottom opening is trapezoidal in shape, with its wider end at the downstream end of the gate furthest from the plane defined by the conveyor, the gate discharge aperture provided between the gate segments in either the operating position or the clean out position is trapezoidal in shape, with its wider end furthest from the plane defined by the conveyor and the linkages both supporting the gate segments and coordinating the movement of the gate segments provide differential movement of the gate segment ends without imposing significant torsional stress on the gate segments.
Preferably, the gate also includes two shear plates, each attached to the downstream end of each gate segment and which overlaps with the shear plate at the downstream end of the other gate segment at all three positions for the gate segments, and which control the maximum height of particulate solid material deposited onto the moving conveyor. More preferably, the distance between the bottom edge of the shear plates and the conveyor belt is sufficient to allow the particulate solid deposited onto the conveyor to adopt its normal repose angle. Additionally, the gate also includes sealing plates attached to the upstream ends of each of the gate segments.
Preferably, the conveyor is provided with a variable speed drive means, and a drive means speed controller.
Preferably, in a sequence of discharge gates, the gate longitudinal axes are all inclined at the same angle, and the upstream ends of the gates are all substantially the same distance from the plane defined by the conveyor.
Preferably, the width of the gate opening provided when the gate segments are moved to the operating position is at least 1.5 times the average particle size of a particulate solid material contained in the hopper.
Preferably, the gate supporting linkages, coordinating means and supporting structures having a first frame means adjacent a first end of the gate aperture and a second frame means adjacent a second end of the gate aperture. A pair of first linkage means including pairs of linkage arms, the arms in each pair being rotatably attached at one end to the first frame means, and at the other end to spaced apart locations at each first end of the gate segments, and a pair of second linkage means including pairs of linkage arms, the arms in each pair being rotatably attached at one end to the second frame means, and at the other end to spaced apart locations at each second end of the gate segments are also included. Furthermore, the gate supporting linkages, the coordinating means and the supporting structures include a first gear means attached to the first linkage means in cooperating relationship between each pair of first linkage means, a second gear means attached to the second linkage means in cooperating relationship between each pair of second linkage means, a first gate segment actuating means connected between each first end of the gate segments, and a second gate segment actuating means connected between each second end of the gate segments. The direction of travel of the conveyor is from the first ends of the gate segments toward the second ends of the gate segments and the linkage arms in the first linkage means are each shorter than the linkage arms at the same positions in the second linkage means by an amount sufficient to minimise any torsional stress placed on the gate segments when the gate is moved between its closed, operating, and clean out positions.
Preferably, the gear means is located between one arm of a pair of arms attached to first gate segment, and the adjacent arm of a second pair of arms attached to the second gate segment. More preferably, the gear means comprises a first gear segment incorporated in one arm of a pair of arms attached to first gate segment; a first rotatable gear meshed with the first segment; a second rotatable gear meshed with the first gear; and a second gear segment attached to the adjacent arm of a second pair of arms meshed with the second gear.
Preferably, within each pair of arms, the arms are of differing length so that the gate segments slope downwardly toward the conveyor when the gate is opened.
Alternatively, the gate supporting linkages, coordinating means and supporting structures having first frame means adjacent a first end of the gate aperture and a second frame means adjacent a second end of the gate aperture. A first pair of support plate means including a first member each being attached at one end to each first end of the gate segments and rotatably at the other end to spaced part locations on the first frame means and a second pair of support plate means including a second member each being attached at one end to each second end of the gate segments and rotatably at the other end to spaced part locations on the second frame mean are also included. Furthermore, the gate supporting linkages, the coordinating means and the supporting structures include at least one gate segment movement coordinating means comprising a first link, a second link and a third joining link, each of which links has a first end and a second end and a support shaft. The first end of the first link is rotatably attached to the first member of the first pair of support plate means, the second end of the first link is rotatably attached to the first end of the third joining link, the second end of the third joining link is rotatably to the first end of the second link, the second end of the second link is rotatably attached to a second member of the second pair of support plate means, the first and second links are of substantially the same length and the third joining link is slidably attached to the shaft by a sliding engagement means constructed and arranged to maintain the third joining linkage substantially perpendicular to the shaft.
Preferably, the first and second links are the same length, and are longer than the third link. More preferably, the first and second links are the same length, and are both about twice as long as the third joining link.
Preferably, the shaft is round and the sliding engagement means comprises a tubular sleeve.